The objective of this research is to define the organization and interrelationships between those components of the central autonomic nervous system which are involved in the control of the circulation. This entails: 1) development of a wiring diagram depicting the specific connections of those neuronal elements which form central cardiovascular circuits; 2) study of the relationships between electrical activity and functional output of these circuits; 3) elucidation of those mechanisms controlling transmission in each of the parallel circuits which may exist; and 4) identification of the mediators within these circuits and the mechanisms of action of drugs which are known to affect transmission of impulses in central cardiovascular pathways. Experiments will be performed on cats. Computer techniques (autocorrelation; post-stimulus and time-interval histogram; spectrum analysis; summation) will be used to analyze population responses of peripheral sympathetic nerve bundles and the activity of single brain stem and spinal neurons as related to ongoing cardiovascular events.